Developmental Dysplasia of the Hip

The hip is a "ball-and-socket" joint. In a normal hip, the ball at the upper end of the femur (thighbone) fits firmly into the socket, which is a curved portion of the pelvis called the acetabulum. In a young person with hip dysplasia, the hip joint has not developed normally—the acetabulum is too shallow to adequately support and cover the head of the femur. This abnormality can cause a painful hip (often initially due to tearing of the labrum at the rim of the acetabulum) and the early development of osteoarthritis, a condition in which the articular cartilage in the joint wears away and bone rubs against bone.

Adolescent hip dysplasia is usually the end result of developmental dysplasia of the hip (DDH), a condition that occurs at birth or in early childhood. Although infants are routinely screened for DDH, some cases remain undetected or are mild enough that they are left untreated. These patients may not show symptoms of hip dysplasia until reaching adolescence. In the United States, approximately 1 to 2 babies per 1,000 are born with DDH. Paediatricians screen for DDH at a newborn's first examination and at every well-baby checkup thereafter.

Treatment for adolescent hip dysplasia focuses on relieving pain while preserving the patient's natural hip joint for as long as possible. In many cases, this is achieved through surgery to restore the normal anatomy of the joint and delay or prevent the onset of painful osteoarthritis. Surgery may also be indicated to deal with early damage to the labrum or acetabular rim cartilage.

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(Left) In a normal hip, the head of the femur fits firmly inside the hip socket. (Right) In severe cases of DDH, the thighbone is completely out of the hip socket (dislocated).

Description

In patients with hip dysplasia, the acetabulum is shallow, meaning that the ball, or femoral head, cannot firmly fit into the socket.  As a result of this abnormality, the way that force is normally transmitted between the bone surfaces is altered. The labrum can end up bearing the forces that should normally be distributed evenly throughout the hip joint. In addition, more force is placed on a smaller surface area of the hip cartilage and labrum. Over time, the smooth articular cartilage becomes frayed and wears away and the labrum becomes torn or damaged. These degenerative changes can progress to early osteoarthritis.

The magnitude and severity of hip dysplasia can vary from patient to patient. In mild cases, the head of the femur may simply be loose in the socket. In more severe cases, there may be complete instability in the joint and/or the femoral head may be completely dislocated out of the socket.

Cause

Adolescent hip dysplasia usually results from developmental dysplasia of the hip (DDH) that is undiscovered or untreated during infancy or early childhood.

DDH tends to run in families. It can be present in either hip and in any individual. It usually affects the left hip and occurs more often in:

• Girls
• First-born children
• Babies born in the breech position
• Oligohydramnios (low levels of amniotic fluid in utero).

Symptoms

Hip dysplasia, itself, is not a painful condition. However, pain results when the altered forces in the hip cause degenerative changes to occur in the articular cartilage and the labrum.  In most cases, this pain is:

• Located in the groin area, although it may sometimes be more toward the outside of the hip, and occasionally in the buttock region
• Occasional and mild initially, but may increase in frequency and intensity over time
• Worse with activity or near the end of the day

Some patients may also experience the feeling of locking, catching, or popping within the groin, and more rarely a description of unstable or unreliable feelings. In more severe high hip dysplasia or dislocation, a leg length inequality may be seen.

Imaging Studies

In most cases, adolescent hip dysplasia can be diagnosed with just a physical exam. Imaging studies are needed to help confirm the diagnosis and aid planning any intervention.

• X-rays. These provide images of dense structures such as bone, and will help A/Prof Woodgate assess the alignment of the acetabulum and femoral head. An x-ray can also show signs of arthritis.
• Computed tomography (CT) scans. More detailed than a plain x-ray, CT scans can help your doctor establish the degree of dysplasia.
• Magnetic resonance imaging (MRI) scans. These studies can create better images of the body's soft tissues. An MRI can help A/Prof Woodgate identify damage to the labrum and articular cartilage.

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(Left) This x-ray shows two normal hips. (Right) This x-ray shows a dysplastic hip. The hip socket is shallow and there is only partial coverage of the femoral head.

Treatment

Treatment for adolescent hip dysplasia focuses on delaying or preventing the onset of osteoarthritis while preserving the natural hip joint for as long as possible. In the (younger) adult, prior to arthritis developing, treatment is more aimed at relieving mechanical symptoms, and without potentially impacting on future surgery, such as hip replacement.

Nonsurgical Treatment

Nonsurgical treatment is indicated when there is only mild hip dysplasia and no damage to the labrum or articular cartilage. Nonsurgical treatment may also be tried initially for patients who have such extensive joint damage that the only surgical option would be a total hip replacement.

Common nonsurgical treatments for adolescent hip dysplasia include:

• Observation. If there are minimal symptoms and mild dysplasia, simply monitoring of the condition may be suggested to make sure it does not get worse. Follow-up follow-up visits every 6 to 12 months are arranged to check for any progression that may warrant treatment.
• Lifestyle modification includes avoiding the activities that cause the pain and discomfort. Losing weight will also help to reduce pressure on the hip joint.
• Physical therapy. Specific exercises can improve the range of motion in the hip and strengthen the muscles that support the joint. This can relieve some stress on the injured labrum or cartilage.
• Medications. Nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen and naproxen, can help relieve pain and reduce swelling in an arthritic joint. In addition, cortisone is an anti-inflammatory agent that can be injected directly into a joint. Although an injection of cortisone can provide pain relief and reduce inflammation, the effects are temporary.

Surgical Treatment

Surgery is recommended if there is ongoing pain that has not responded to conservative nonsurgical management. The surgical procedure most commonly used to treat hip dysplasia is an osteotomy. "Osteotomy" literally means "cutting of the bone." In an osteotomy, the surgeon reshapes and reorients the acetabulum and/or femur so that the two joint surfaces are in a more normal anatomic position.

There are different types of osteotomies that can be performed to treat hip dysplasia. The specific procedure recommended will depend on a number of factors, including:

• Age
• The severity of the dysplasia
• The extent of damage to the labrum
• Whether osteoarthritis is present
• The number of remaining growing years (in a child or adolescent)

Periacetabular osteotomy (PAO).  Currently, the osteotomy procedure most commonly used to treat adolescent hip dysplasia is a periacetabular osteotomy (PAO). "Periacetabular" means "around the acetabulum." In most cases, PAO takes from 2-3 hours to perform. During the surgery, four cuts are made in the pelvic bone around the hip joint to mobilise the acetabulum.  The acetabulum is then rotated and repositioned it into a more normal anatomic position over the femoral head.  X-rays are used intra-operatively to direct the bony cuts and to ensure that the acetabulum is repositioned correctly. Once the bone is repositioned, several screws are inserted to hold it in place until it heals. 

As with any surgical procedure, there are risks involved with PAO. These risks will be discussed with you. Although the risks are low, the most common complications include:

• Infection
• Blood clots
• Injuries to blood vessels and nerves
• Persistent hip pain
• Failure of the osteotomy to heal

Arthroscopy.  In conjunction with, or as an alternative option to PAO, hip arthroscopy may be recommended to repair or debride (tidy up loose segments by trimming) a torn labrum. During arthroscopy, a small camera, called an arthroscope, in inserted into the joint. The camera displays pictures on a television screen, and these images to guide miniature surgical instruments. Arthroscopic procedures may include:

• Labral refixation. In this procedure, the doctor trims the torn and frayed tissue around the acetabular rim and reattaches the torn labrum to the bone of the rim.
• Debridement. In some cases, simply removing the torn or weakened labral tissue can provide pain relief.

Hip Replacement.  Once more conservative interventions have failed, or more significant arthritis has developed, the most reliable solution is hip replacement.  A/Prof Woodgate will discuss at length the timing of when this procedure should be done, the approach to be utilised, specific implants required, as well as the benefits, risks, complications, and likely outcomes.